1. Field of the Invention
The present invention relates to a difference image generation device that generates an output image signal in which a difference between input image signals is reflected.
2. Description of Related Art
TOMITA (Japanese Unexamined Patent Application Publication No. 09-128534) discloses an image processing device which facilitates the image quality evaluation for evaluating image signals subjected to image processing. The device compares two input signals (an original image signal and a measured image signal) and generates an output image signal on which characterization processing is performed so as to enhance the difference between the two input signals. The measured image signal is obtained by performing some image processing on the original image signal. An example of the measured image signal is obtained by expanding a compressed original image signal.
More specifically, the device described in TOMITA generates the absolute value of the difference between the two input signals (the original image signal and the measured image signal) and compares the difference absolute value with a threshold. When the difference absolute value exceeds the threshold, the device multiplies the difference absolute value by a “multiplication coefficient”, to thereby generate a difference absolute value signal. When the difference absolute value is equal to or smaller than the threshold, the value of the difference absolute value signal is zero. Note that the multiplication coefficient, which determines the magnitude of the difference absolute value signal, is specified by a user.
The device described in TOMITA then adds an “offset amount” to the difference absolute value signal, thereby generating a “characterizing image signal”. The offset amount is also specified by the user. Lastly, when the value of the difference absolute value signal is zero, i.e., when the absolute value of the difference between the two input images is equal to or smaller than the threshold, the device selects one of the two input signals (e.g., the original image signal) and outputs the selected signal as the output image signal. Meanwhile, when the absolute value of the difference between the two input images exceeds the threshold, the characterizing image signal is output as the output image signal in place of the input image signal.